An air pressure regulator provides a fluid pressure output which varies with an input signal. Pressure regulators have many usages which require that the regulated pressure be very accurately controlled. One example is in the testing of pneumatic instruments such as an air speed indicator, an altimeter, and a rate of descent meter for an aircraft. It is also necessary to test the systems in which these instruments are used. The test must accurately simulate the air pressure these instruments encounter during actual inflight conditions, and this requires that the air pressure regulator provide air pressure above and below ambient pressure.
One prior art system for pressure regulators utilizes two regulators, one for pressures above ambient and one for pressures below ambient. Each regulator uses a flexible, resilient, valve strip folded between a swing arm and a port. By pivoting the swing arm, the valve strip is moved to progressively close or open the port. The differential pressure across the port tends to seat the valve strip against the surface surrounding the port.
The use of a folded valve strip is most effective in a pressure regulator. Unfortunately, the prior art system described above requires two of the regulators, and this substantially increases the cost and complexity of the system.